Field of the Invention
The present disclosure relates to AC motors. More particularly, the present disclosure relates to systems comprising an AC motor configured to be started with a variable speed drive and then transferred to a higher voltage power system. An AC motor of this configuration, methods of manufacturing such an AC motor, and methods of operating such an AC motor are also embodiments of the invention.
Description of Related Art
Many industrial applications of AC motors require starting high load torques with minimal impact in the power system. Attempts to meet these demands have included reduced voltage soft starters, autotransformers, inductors, and combinations of inductor and capacitor starters, but these have the disadvantage of not providing the full motor torque capability at low speed. With the exception of reduced voltage soft starters, these solutions also introduce important transients in line currents and motor air-gap torque during the switching events. Various system and motor configurations exist but do not solve these issues, including U.S. Pat. No. 8,471,426, European Patent No. 2341247, and European Patent No. 1267473.
It has been found that use of a variable speed drive partially addresses these starting problems by changing the output frequency and voltage such that it is able to control the motor torque from zero to maximum speed. However, in some cases the maximum voltage available at the output of the variable speed drive is lower than the available system voltage. For the industrial applications described above, when the maximum output voltage of the variable speed drive is lower than the system nominal voltage, a step-up transformer is required between the variable speed drive output and the motor terminals. However, these step-up transformers take space and add an important installation and operating cost to the system. Thus, there is a need for improved methods and systems that overcome these limitations.